This invention relates to a two-stage process for coloring keratin fibers and to the use of a special pretreatment composition in this process.
Preparations for tinting and coloring hair are an important type of cosmetic product. They may be used to give the natural color of the hair a light or relatively dark shade, to obtain a totally different hair color or to cover unwanted color tones, for example gray tones, according to the wishes of the particular user. Conventional hair colorants are formulated either on the basis of oxidation dyes or on the basis of substantive dyes according to the required color or the permanence thereof. In many cases, combinations of oxidation dyes and substantive dyes are also used to obtain special shades.
Colorants based on oxidation dyes lead to brilliant and permanent color tones. However, they do involve the use of strong oxidizing agents, such as hydrogen peroxide solutions for example. Colorants such as these contain oxidation dye precursors, so-called primary intermediates and secondary intermediates. The primary intermediates form the actual dyes with one another or by coupling with one or more secondary intermediates under the influence of oxidizing agents or atmospheric oxygen.
Colorants based on substantive dyes do not require oxidizing agents and may be formulated at pH values near the neutral point. A major disadvantage of colorants based on substantive dyes is the poor fastness to washing of the colors obtained. In many cases, the capacity of the dye molecules for absorption onto the hair and the shine of the colored hair are not entirely satisfactory either.
Nevertheless, these known coloring methods are still not totally convincing. In many cases, an uneven color impression is created after coloring, particularly with the so-called fashionable shades in the red, copper and gold range, the hair fibers showing a loss of brilliance at their tips. This unevenness of coloring is attributable to the different care states of the hair fibers in the freshly regrown parts and the tips which may have become more porous through previous treatments or environmental influences. Accordingly, the problem addressed by the present invention was to provide a coloring process for keratin fibers which would not have the disadvantages mentioned above and which would lead to colors with excellent fastness properties.
It has now surprisingly been found that highly uniform colors with excellent fastness properties—even in the case of fashionable red, copper and gold shades—can be obtained if the fibers are treated in a first step with a pretreatment composition containing substantive dyes and are subjected in a second step to conventional coloring with at least one synthetic dye (precursor).
Two-stage processes for coloring keratin fibers have been known for some time. WO 90/01922-A1, for example, discloses a hair coloring process in which the hair is treated in a first step with a preparation containing a substantive dye and in a second step with a preparation containing natural dyes. However, there is nothing in that document which points to the advantages of the process according to the present invention. In many cases, such coloring processes were very complex and could only be carried out by professionals. In addition, the colors obtained with such processes were still not entirely satisfactory in regard to evenness and fastness.